1. Field of the Invention
This invention relates to a method for recompleting a cased wellbore using through-tube rotary drilling.
2. Brief Description of the Prior Art
Many oil fields are produced by drilling a wellbore to extend from a surface into an oil bearing formation, casing the wellbore from the surface to or through the oil bearing formation, perforating the casing if it extends through the oil bearing formation, to provide fluid communication between the interior of the casing and the oil bearing formation and positioning a production tubing string in the casing to extend from a depth in or slightly above the oil bearing formation to the surface for the production of fluids from the oil bearing formation. Such wells are used to produce fluids such as oil, gas, water and mixtures thereof from subterranean oil bearing formations under the formation pressure. In other instances, a pump may be used to cause the fluids to flow to the surface. After a period of production, the oil bearing formation surrounding the wellbore becomes depleted so that fluids do not flow into the wellbore and upwardly through the tubing for production. In such instances, a pump may be lowered through a smaller tubing into the formation and fluids may then be pumped to the surface until the flow of fluids from the oil bearing formation stops or drops to an uneconomical level.
In many instances, other areas of the oil bearing formation in the vicinity of the wellbores may not be depleted. Unfortunately, it is expensive to remove the tubing and sidetrack the well through the existing well casing using conventional sidetracking methods. Such methods require that the tubing be removed, a section of the casing be milled out and a drill be run back down through the casing and directed outward through the milled-out section to drill a directional well from the casing outwardly to an area from which additional hydrocarbons may be recovered. Since these techniques are relatively expensive, the amount of potential hydrocarbon recovery required to justify such sidetracking operations is relatively large. Since, in many instances, areas of potentially recoverable hydrocarbons containing less than the amount required to justify this additional expense are known, it is desirable that a more economical method be developed to enable the economical recovery of these smaller quantities of hydrocarbons. The smaller quantities of hydrocarbons may, in fact, be quite sizeable.
One method which has been used in an attempt to reach such hydrocarbons is the use of coiled-tubing drilling. By this method, coiled tubing is used to pass a drill downwardly through the existing tubing and outwardly through an opening in the well casing and drilling a directional well to reach additional hydrocarbons. The use of coiled tubing permits the use of a liquid-driven motor (mud motor) drill supported on coiled tubing. The coiled tubing is not rotatable and is subject to sliding friction and sticking in the existing tubing in the wellbore, the drilled well, and the like. As a result, this method is limited in the length of holes that can be drilled because of the sliding friction of the non-rotatable coiled tubing.
Since, in many instances, drilling to greater distances than previously reachable by the use of coiled tubing is necessary, a continuing effort has been directed to the development of an improved method whereby additional hydrocarbons can be reached.